The present invention relates to a process of forming an interconnection of a semiconductor device and a sputtering system therefor.
The higher integration of semiconductor devices requires the design rule of finer-geometries, and to meet such a requirement, interconnections of semiconductor devices are also required to be formed at a high reliability, particularly at a high electromigration resistance. In particular, for an interconnection layer typically made of aluminum or an aluminum alloy (hereinafter, referred to generally as "an aluminum based alloy"), it is well known that the electromigration resistance thereof is strongly dependent on the degree of crystal orientation of the aluminum based alloy layer along the (111) face or the crystal particle size thereof [see "Improvement in the Electromigration Lifetime Using Hyper-Textured Aluminum Formed on Amorphous Tantalum-Aluminum Underlayer," H. Toyoda, et al.,THE 32TH IRPS, IEEE, p178-184 (1994) and "Effects of Grain Size and Preffered Orientation on the Electromigration Lifetime of Al-based layered Metallization," Seiichi Kondo, et al., Journal of Applied Physics, 78, p6534-6538 (1995)].
The finer-geometries of an interconnection possibly causes stress-migration in which the interconnection is disconnected due to stress applied from an insulating layer. To prevent occurrence of stress-migration, there has been generally adopted a so-called laminated metal structure. In this structure, a layer having a high yield stress, which is made of a high melting point metal such as Ti or a high melting point metal compound such as TiN or a conductive metal layer or metal compound layer, is previously formed under an interconnection made of an aluminum based alloy, whereby disconnection of the entire interconnection is prevented by the redundant effect of such a layer. This redundant effect will be shown in FIG. 9. In addition, a high melting point metal layer or the like formed under an interconnection made of an aluminum based alloy is hereinafter referred to generally as "a metal backing layer".
It becomes apparent that the crystal orientation of an aluminum based alloy is largely dependent on the crystal orientation of a metal backing layer and a lattice conformity with crystals of the metal backing layer. In particular, titanium (Ti) generally used for a metal backing layer has the (0002) face as the priority orientation face which is good in lattice conformity with the (111) face of crystals of aluminum. It is reported that as the degree of crystal orientation of a metal backing layer of Ti along the (0002) face becomes higher, the degree of crystal orientation of an aluminum based alloy layer formed thereon along the (111) face becomes higher [see "Formation of Texture Controlled Aluminum and Its Migration Performance in Al--Si/TiN Stacked Structure," Makiko Kageyama, et al.,The 29th IRPS, IEEE, p97-101 (1991)]. The same is true for the case where a TiN layer having crystals orientated along the (111) face is formed between the Ti layer and the aluminum based alloy layer. That is, for a metal backing layer having a laminated structure of Ti/TiN, as the degree of crystal orientation of the metal backing layer becomes higher, the degree of crystal orientation of an aluminum based alloy layer formed thereon along the (111) face becomes higher. As a result, the reliability of an interconnection made of such an aluminum based alloy layer can be enhanced.
The degree of crystal orientation of a metal backing layer is largely affected by a surface state of an insulating layer on which the metal backing layer is to be formed. In general, for ensuring electric connection with a connection hole such as a contact hole or a via-hole, the surface of an insulating layer is subjected to sputter-etch cleaning before formation of a metal backing layer. And, a metal backing layer and an aluminum based alloy layer are deposited at a reduced pressure by sputtering using the same system.
When the surface of an insulating layer mainly containing SiO.sub.2 is subjected to sputter-etch cleaning, a Si-rich layer is formed on the surface of the insulating layer. In this case, if a metal backing layer is made of titanium, a thin film made of a Ti--Si--O based material being rich in Ti, which is similar to silicide, is formed near the boundary between the insulating layer and the metal backing layer [see "Influence of Under-metal Planes on Al (111) Crystal Orientation in Layered Al Conductors", H. Shibata, et al., 1991 VLSI Symp. pp33-34]. Ti atoms are easily re-arranged at the step of forming such a thin film, and consequently Ti crystals are strongly orientated along the (0002) face as the priority orientation face. As a result, the degree of crystal orientation of an aluminum based alloy layer becomes higher. The reliability of an interconnection made of such an aluminum based alloy layer can be thus enhanced.
However, in the case where the atmosphere contains oxygen in a high concentration upon sputter-etch cleaning and in a period until a metal backing layer is formed, a Si-rich layer formed on the surface of the insulating layer upon sputter-etch cleaning is immediately re-oxidized. In particular, since temperature rise due to plasma is given upon sputter-etch cleaning, discharge of gas from an insulating layer and various jigs provided in the sputter-etch cleaning chamber becomes higher, and thereby the Si-rich layer on the surface of the insulating layer is liable to be re-oxidized. As a result, it is hard to form a thin layer made of a Ti--Si--O based material being rich in Ti near the boundary between the insulating layer and metal backing layer. Thus, there occurs a problem that the degree of crystal orientation of the aluminum based alloy layer along the (111) face is lowered.